A Compact Inductively Coupled Connector for Mobile Devices Wenxu Zhao, Peter Gadfort, Evan Erickson, Paul D. Franzon North Carolina State University Introduction A nested inductive connector, consisting of a single power channel and one or more data channels, is proposed as replacement for legacy conductive connectors in mobile devices. As an example, a prototype of the proposed connector was designed as a replacement for a standard TRS headphone jack found on many mobile devices. Motivation Acknowledgements The authors would like to thank Dr. John Wilson for his valuable suggestions on power supply design and implementation. Prototype Design Results & Conclusion Losses in an inductively coupled channel can generally be minimized by increasing the diameter of the inductor, increasing the number of turns in the inductor. By increasing the number of turns, and consequently the diameter of the inductor, the frequency at which peak coupling occurs decreases and the peak increases. Low profile: as thin as a PCB Breaks away to avoid stress damage Waterproof Connector Design Forward transfer coefficients (S 21 ) for the proposed connector’s power inductor as turns are varied Forward transfer coefficients (S 21 ) for the proposed connector’s data inductor as turns are varied Effect of increasing the gap between the two mating connectors on the power channel Effect of increasing the gap between the two mating connectors on the data channel Designed and fabricated in IBM 0.13um CMOS technology Input digital stereo audio sampled at 44.1 kHz with 16 bits resolution Processing of audio data:  Sending sampled digital audio data across the high-pass inductive data channel  Recovery of the data on the receiver side  Converting the digital data to power amplified analog audio signal with Class-D PA to output 12mW on each 32Ω load The power recovered from the power transformer is converted from AC to DC power using a two-stage differential-drive CMOS rectifier, producing a stable 1.2 V supply ANSYS HFSS model of the prototype connector with a 2-turn power inductor and a 3-turn data inductor 100um Metal Width 500um Diameter via 3mm by 3mm dimension Technology IBM 0.13 μm CMOS Area1 mm x 1 mm Power Dissipation TX3 mW RX1 mW Deserializer200 μW Alignment100 μW Clock Recovery 400 μW PWM Generator 400 μW Output Buffer (include load) 50 mW Max Data Rate2 Gbps PWM Output for a 5 kHz toneFrequency spectrum for the 5 kHz output Inductive headphone driver performance metrics Requires significant space Easily bent when stressed Not waterproof Legacy TRS Connector Proposed Connector Space is at a premium in modern mobile devices as manufactures strive to make the thinner, lighter devices with the longest battery lives possible. By transitioning from legacy connectors, TRS audio jacks, to a low-profile inductively coupled connector for the transmission of both power and high-speed data, space inside the mobile device can be conserved while providing an orientation independent, waterproof design that can breakaway when stressed. Another parameter that has significant impact on the connector is the gap between the two mating connectors. In order to maintain a waterproof design, the two connectors would be coated in a thin layer of plastic. As seen in the figures, the separation distance of the connectors has a large impact on the peak in the forward transfer coefficient, but does not shift its frequency. Thus, a connector with embedded circuitry would not have to be redesigned for a specific spacing. Isolation of the power and data channelsIsolation between a pair of data coils in the proposed connector When adding additional channels, sufficient isolation between the channels is required, a connector composed of a pair of 2-turn data coils within a 2-turn power coil was simulated while varying data-to-data spacing. To study the effect of crosstalk between the power and the data channel, the spacing between a 2-turn power inductor and a 2-turn data inductor was varied from 0.5 mm to 1.25 mm. The complete design was simulated using a single tone of 5 kHz, which is sampled at 44.1 kHz with a resolution of 16- bits. The transient simulation results, as presented on the left, shows the PWM output voltage across the 32  load, while figure on the right shows the corresponding frequency spectrum. The 5 kHz tone is recovered, however distortion at the harmonics of the input frequency is present, but can be mitigated by implementing an algorithm based PWM generation process instead of uniform sampling and implementing a feedback loop in the power amplifier